This renewal application represents a continuation of work on the control of gene expression in the parasitic protozoa, Leishmania enriettii. There are two major goals in our proposed project: 1) to understand the mechanism of transcriptional regulation in the parasite and define the function of DNA sequences involved in this regulation, and 2) to understand the role of RNA transsplicing in the regulation and expression of mRNA in the parasite. The genes for alpha and beta tubulin which are developmentally regulated in their expression in the parasite will be used as a model system for this study. They were cloned and characterized during the previous grant period. To accomplish these goals, it will be necessary to develop a transfection system for the functional analysis of DNA or RNA sequences by in vitro mutagenesis. A transient expression system has now been developed in our laboratory. It is the first to be described for protozoan parasites. This discovery will now be used to accomplish the aims of the grant.